l82 



NATURE 



[Dec. 2 2, i6by 



while the oxygen is set free, and a considerable quantity 

 of it is converted into the more condensed form of ozone. 



On taking the apparatus to pieces after each experi- 

 ment, the hydrofluoric acid remaining was found to con- 

 tain a small quantity of platinum fluoride in solution, and 

 a black mud consisting of a mixture of iridium and pla- 

 tinum in suspension. The negative electrode was not 

 attacked, but the platinum rod forming the positive pole 

 was eaten away to a point, so that one rod only served 

 for two experiments. The average delivery of gas was 

 about I "5 to 2 litres per hour. 



With regard to the chemical processes involved in the 

 electrolysis, it appears probable that potassium fluoride is 

 first decomposed into fluorine, which is evolved at the 

 positive pole, and potassium, which decomposes hydro- 

 fluoric acid, liberating its equivalent of hydrogen at the 

 negative pole, and re-forming potassium fluoride, which 

 may again be electrolyzed. Hence a small quantity of 

 the double fluoride can serve for the decomposition of a 

 comparatively large amount of hydrofluoric acid. 



The double fluoride HF. KF is very soluble in hydro- 

 fluoric acid, forming a crystallizable compound, richer in 

 hydrofluoric acid than HF. KF, and which gives off no 

 acid vapour at the boiling-point of the anhydrous acid, 

 I9°'4. It is this compound which one ought to seek to 

 obtain for electrolysis, as it is very soluble in excess of 

 acid, forming a hquid of good conductivity. 



The double fluoride HF. KF itself was finally electrolyzed 

 by M. Moissan. It fuses at 140° to a colourless liquid 

 which is quite suitable for electrolysis. The experiment 

 was performed, as before, in a platinum U-tube, and, on 

 passing the current, fluorine was again liberated at the 

 positive pole, and at once set fire to crystalline silicon ; 

 but the platinum was strongly attacked, so the experiment 

 was stopped in orderto save the tube. On plunging a couple 

 of platinum wires connected with the battery into a quan- 

 tity of the fused double fluoride contained in a platinum 

 crucible, gas was evolved in abundance at each pole, and 

 on bringing the wires in contact, even in the dark, de- 

 tonation occurred, owing to the combination of the evolved 

 hydrogen and fluorine. At the same time the platinum 

 wire from which the fluorine was evolved was almost 

 entirely eaten away. 



In concluding these remarkable researches, which have 

 happily terminated so successfully, M. Moissan discusses 

 very fully the question of the identity of the gas liberated 

 at the positive pole with the element fluorine ; and there 

 can be no doubt that he has completely proved this 

 identity, at the same time showing that fluorine occupies 

 the place of honour as the most intensely active chemical 

 element with which we are at present acquainted, and 

 that it assumes its rightful position, theoretically destined 

 for it, at the head of the group of halogens. 



A. E. TUTTON. 



TIMBER, AND SOME OF ITS DISEASES. 



I. 



r'\ N carefully examining the clean-cut end of a sawn log 

 ^-^ of timber, it is easy to convince ourselves of the 

 existence of certain marks upon it, which have reference 

 to its structure. These marks will vary in intensity and 

 number according to the kind of tree, the age at which it 

 is felled, and some other circumstances, which may be 

 overlooked for the present ; but in a given case it would 

 be possible to observe some such marks as those indicated 

 in Fig. I. In the specimen chosen there is a nearly 



central spot, the pith, around which numerous concentric 

 lines — the " annual rings " — run. Radiating from the pith 

 towards the periphery are cracks, the number, and length, 

 and breadth of which may vary according to the time the 

 log has been exposed to the weather, and other circum- 

 stances ; these cracks are due to the contraction of the 

 wood as it " shrinks," and they coincide with medullary 

 rays, as lines of weakness. Between these cracks are to 

 be seen numerous very fine radiating lines indicating the 

 course of the uninjured medullary rays, which again 

 will vary in distinctness, &c., according to the species of 

 timber. 



Fig. I.— a log of timber, showing radial cracks after lying exposed for some time, a, a large crack extending from pith to 

 circumference ; b, the cortex ; c, medullary ray ; d, cambium ; e, annual ring ; f, outer bark, proper. Reduced. 



This log of wood, with its annual rings and medullary 

 ray's, is clothed by a sort of jacket, consisting of cork and 

 softer tissues, and termed the cortex, or, more popularly, 

 the " bark " (an unfortunate word, which has caused much 

 trouble in its time). The largest of the cracks is seen to 

 traverse the whole radiug of the face of the wood from 

 centre to circumference, and also to pass through the 

 cortex, which gapes widely. 



The remaining cracks, however, stop short at a line 

 which marks on the one hand the inner face of the cortex, 

 -md on the other the outer face of the wood : this line also 

 represents the cambium, a thin sheet of generative tissue 



which remains after giving rise to practically the whole 

 of the wood (a very little in the centre excepted) and cortex 

 visible in the woodcut. Since we are not concerned with the 

 cortex and bark at present, it will be convenient to regard 

 the log as " barked," and only deal with the wood or timber ^ 

 itself, in the condition to which the woodman reduces 

 after removing the cortex with certain implements. 



If now we split such a log as Fig. i along the line 

 the big crack, neatly and smoothly, the well-known 

 " grain " so often observed on planks of wood will come 

 into view, and it will be noticed that the lines which mark 

 the "o^raiii" are continuations of the lines which mark 



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